package com.yisu.expressway.utils;


import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;

public class MD5Util {   
    /**  
     * 默认的密码字符串组合，用来将字节转换成 16 进制表示的字符,apache校验下载的文件的正确性用的就是默认的这个组合  
     */  
    protected static char hexDigits[] = { '0', '1', '2', '3', '4', '5', '6',   
            '7', '8', '9', 'a', 'b', 'c', 'd', 'e', 'f' };   
  
    protected static MessageDigest messagedigest = null;   
    static {   
        try {   
            messagedigest = MessageDigest.getInstance("MD5");   
        } catch (NoSuchAlgorithmException nsaex) {   
            System.err.println(MD5Util.class.getName()   
                    + "初始化失败，MessageDigest不支持MD5Util。");   
            nsaex.printStackTrace();   
        }   
    }   
       
    /**  
     * 生成字符串的md5校验值  
     *   
     * @param s  
     * @return  
     */  
    public static String getMD5String(String s) {   
       return getMD5String(s.getBytes());   
    }   
       
    /**  
     * 判断字符串的md5校验码是否与一个已知的md5码相匹配  
     *   
     * @param password 要校验的字符串  
     * @param md5PwdStr 已知的md5校验码  
     * @return  
     */  
    public static boolean checkPassword(String password, String md5PwdStr) {   
       String s = getMD5String(password);   
        return s.equals(md5PwdStr);   
    }   
       
    /**  
     * 生成文件的md5校验值  
     *   
     * @param file  
     * @return  
     * @throws IOException  
     */  
    public static String getFileMD5String(File file) throws IOException {          
        InputStream fis;   
        fis = new FileInputStream(file);   
        byte[] buffer = new byte[1024];   
        int numRead = 0;   
        while ((numRead = fis.read(buffer)) > 0) {   
            messagedigest.update(buffer, 0, numRead);   
        }   
        fis.close();   
        return bufferToHex(messagedigest.digest());   
    }   
    
    public static String getMD5String(byte[] bytes) {
        messagedigest.update(bytes);   
        return bufferToHex(messagedigest.digest());   
    }   
  
    private static String bufferToHex(byte bytes[]) {   
        return bufferToHex(bytes, 0, bytes.length);   
    }   
  
    private static String bufferToHex(byte bytes[], int m, int n) {   
        StringBuffer stringbuffer = new StringBuffer(2 * n);   
        int k = m + n;   
        for (int l = m; l < k; l++) {   
            appendHexPair(bytes[l], stringbuffer);   
        }   
        return stringbuffer.toString();   
    }   
    
    private static void appendHexPair(byte bt, StringBuffer stringbuffer) {   
        char c0 = hexDigits[(bt & 0xf0) >> 4];// 取字节中高 4 位的数字转换, >>> 为逻辑右移，将符号位一起右移,此处未发现两种符号有何不同    
        char c1 = hexDigits[bt & 0xf];// 取字节中低 4 位的数字转换    
        stringbuffer.append(c0);   
        stringbuffer.append(c1);   
    }   
       
}  
